tests: rename duplicate t4205

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/t4205-log-follow-harder-copies.sh b/t/t4206-log-follow-harder-copies.sh
similarity index 100%
rename from t/t4205-log-follow-harder-copies.sh
rename to t/t4206-log-follow-harder-copies.sh